A. Field of the Invention
The present invention relates to a fire-retardant, arc-extinguishing, processed resin article used to extinguish the arc generated from contact points during an interruption in current flow, for example, by a circuit breaker. The present invention further relates to a circuit breaker that uses this fire-retardant arc-extinguishing processed resin article.
B. Description of the Related Art
In a circuit breaker, an arc is generated between contact points when the contact point on the movable contactor is separated from the contact point on the stationary contactor while an overcurrent or rated current is flowing therethrough. In order to extinguish this arc, an arc-extinguishing device is typically disposed on the periphery of the arc-generating region. This arc-extinguishing device is equipped with an arc-extinguishing chamber comprising an arc-extinguishing member. The arc-extinguishing member undergoes pyrolysis under the action of the arc, and the arc is then extinguished by the pyrolysis gas that is generated from the arc-extinguishing member.
Thermosetting resins, e.g., unsaturated polyester resin (Japanese Patent 3,098,042) and melamine resin (Japanese Patent Application Laid-open No. H02-256110), and thermoplastic resins, e.g., polyolefin resin, polyamide resin, and polyacetal resin (Japanese Patent Application Laid-open No. H07-302535 (U.S. Pat. No. 5,841,088)), are primarily used as the matrix resin in this arc-extinguishing member.
However, thermosetting resins are prone to burring during molding and thus have had a molding processability that is inferior to that of thermoplastic resins. In addition, the internal pressure within the arc-extinguishing device rises during arc extinction due to the generation of pyrolysis gas from the arc-extinguishing member. This has made it difficult to reduce the size of the arc-extinguishing device in the case of thermosetting resins, which have a poor pressure resistance.
Thermoplastic resins do resist burring during molding, but they have a poor strength, pressure resistance, and heat resistance and provide an arc-extinguishing member that tends to deform or deteriorate over time. On the other hand, thermoplastic resins that have a high aromatic ring content, such as aromatic polyamide resins, exhibit a relatively good strength, pressure resistance, and heat resistance, but they readily release free carbon during combustion. This has resulted in problems such as a potential carbon-mediated erosion of the arc-extinguishing device and a loss of the insulating characteristics of the arc-extinguishing device.
The addition of a metal hydroxide, e.g., magnesium hydroxide, aluminum hydroxide, and so forth, has also been tried in order to raise the arc-extinguishing performance of thermoplastic resins and thermosetting resins (Japanese Patent 3,098,042 and Japanese Patent Application Laid-open Nos. H02-256110, 07-302535 (U.S. Pat. No. 5,841,088), and 08-171847).
WO 2003/044818 discloses a circuit breaker that employs a processed resin article obtained by treating a thermoplastic resin, e.g., polyester or polyamide, with an electron beam.
Metal hydroxides undergo a dehydration reaction during pyrolysis with the generation of a pyrolysis gas that exhibits a high arc-extinguishing activity. Due to this, the addition of a metal hydroxide to the resin results in an elevated arc-extinguishing performance by the resulting processed resin article, as disclosed in the aforementioned Japanese Patent 3,098,042 and Japanese Patent Application Laid-open Nos. H02-256110, 07-302535 (U.S. Pat. No. 5,841,088), and 08-171847. However, metal hydroxides have a poor compatibility with, and a poor dispersibility in, resins. This is associated with the facile generation of dispersion defects, and as a consequence the resin composition has been prone to exhibit a poor molding processability. In addition, there has been a distinct tendency for fluctuations to be produced in the properties of the obtained processed resin article, for example, in the arc-extinguishing performance, strength, heat resistance, pressure resistance, and so forth.
As disclosed in WO 2003/044818, an improvement in, for example, the strength, heat resistance, and pressure resistance was seen when a crosslinking process was executed on thermoplastic resin. However, no improvement in the arc-extinguishing performance was seen. Moreover, there was also almost no inhibition of the internal pressure increase within the arc-extinguishing device due to the pyrolysis gas generated during arc extinction and the arc-extinguishing device was readily damaged by the internal pressure rise at the time of arc extinction.